Fabricated Microvascular Networks. The importance of an effective vascular supply for tissue health is universally accepted. In developing strategies to build vasculatures for tissue engineering and other therapeutic applications, it is important to recognize that, foremost, the new vasculature must quickly provide sufficient blood flow to the target tissue to preserve cell viability. We have found that new microvessels formed in vitro can begin to carry blood within the first days following implantation. However, flow patterns are atypical and likely ineffective at establishing normoxia until many days later. The delay is primarily due to a lack of organization within the network at the time of implantation and the time needed to develop new mature inflow and outflow pathways. We hypothesize that pre-determining an appropriate network organization prior to implantation would reduce the amount of time needed for the new microvasculature to effectively perfuse a tissue. We have established generic technologies utilizing a direct-write tissue printing tool for patterning and organizing tissue components for tissue engineering applications. We propose to implement this technology to design and fabricate pre-patterned, 3-dimensional microvascular networks with pre-existing inflow and outflow pathways. Also, we will use an in vitro, intravascular-perfusion bioreactor system to establish flow through the networks to further organize and mature the microvascular networks prior to implantation. Computational modeling and physiological analyses serve to direct design strategies and characterize the architectures and functionality of the fabricated vasculatures both in vitro and in vivo. In addition to providing an enabling technology platform for assembling pre-determined microvascular networks, this work will provide a foundation from which to explore the importance of network architectures in vascular function.